1. Field of the Invention
The invention relates to a actuation circuit for an electromagnetic actuator having an electrical time constant and a switching threshold and comprising an energy store connectable to a supply voltage, said energy store being adapted to be connected via at least one switch with the actuator.
2. Description of Related Art
Actuation circuits for electromagnetic actuators are frequently used in the vicinity of explosion-endangered areas, for example in the chemical industry. A typical application are actuators for valves, e.g. linear actuators for shut-off valves. These valves serve for very rapidly switching on or off mass or volume flows in protective systems, or for very rapidly pilot-controlling suitable shut-off devices and thus for carrying out switching actions. Operation of electromagnetic actuators requires supply of very high energies for a short time. When the energy required for the switching action must be fed through the explosion-endangered area, the respective lines must be routed in an explosion-proof manner. This involves a considerable expenditure. It is further common practice to provide an energy store near the actuator, wherein the trigger signal is fed as a relatively weak electrical signal through the explosion-endangered area to the energy store. The energy stores are normally accumulators or capacitor batteries.
It is often necessary to operate actuators very quickly. When, for operating the actuator, an energy store is discharged, this often involves a considerable delay of several seconds. For accelerating the actuating process, the charging voltage of the energy store can be increased. This however increases the danger of explosion in an explosion-endangered environment. Further, there is the danger that the soft-iron core included in an actuator is driven to saturation by too high a voltage. Permanent magnets may become damaged if the coercive force is exceeded.